1. Field of the Invention
The present invention is directed to the screening of granular material and particularly to the sifting of soil. It is particularly directed to a screening method wherein a screening drum or plates are removably fixed on a belt conveyor and located at a low level so that the screened soil is dropped on an upwardly moving tilted conveyor. The conveyor is adapted to drop the sifted soil at its upper end above a truck box body or into a pile for later disposal.
The novel screening arrangement makes use of a novel screening drum which displays a completely free inner space and which rotates on the external surface of two end rings.
The screening arrangement according to the invention has a modular concept which allows the quick and easy interchangeability of the mixed soil receiving bucket and the drum and the substitution of screening plates for the drum.
2. Prior art
A search among prior patents by the applicant, has failed to reveal any pertinent references. In presently available soil screening arrangements, mixed soil is dropped at the lower end of a tilted belt conveyor which brings the soil to a screening drum suspended at the upper end of the conveyor high above the ground. The drum is suspended by an axle extending through its longitudinal axis.
It is well known that soil screening drums produce a considerable amount of flying soil particles when in rotation. Such particles are considerably embarrassing for surrounding workers. When the rotating drum is located high above the ground, the dust produced by the flying soil particles is susceptible of being spread over a greater distance. This distance is further increased by the wind which has a stronger effect on the particles flying at a higher level. Generally, such a problem needs to be controlled by fences or tarpolins when dwellings are located within such vicinity.
Furthermore, the prior soil screening drums are rotated by driving a central longitudinal axles which is supported by radial rods fixed to the cylindrical periphery of the drum. These rods prevent the free longitudinal passage of the mixed soil especially when the later contains large tree roots which get stuck inside the drum or damages the later. The removal of the roots or the repair of the drum is slow, time consuming and lowers the productivity of the process, particularly due to the fact that such axially driven drums require numerous hours of labor for their removal and installation.